This invention relates an automatic exposure control and light source control device for an endoscope photographic system for taking internal pictures of living body tissue.
Although lighting the object is essential for internal body photography with an endoscope, the operating conditions of the light for this purpose are limited. More specifically, a relatively high speed shutter control is required for obtaining an image which is both clear and sharp, and for this purpose it is essential to brightly illuminate the object. However, as a strong light source has a damaging thermal influence on body tissue, a photographic synchronization type lighting system in which the light source is only exposed for the short period of time necessary for the photographing has been employed in this art. In the conventional synchronization type lighting system, a light source side shutter is provided in addition to the camera shutter. The object illumination is effected only when the film is exposed, or from immediately before to just after the film exposure, by a device which, with the camera shutter opened, opens and closes the light source side shutter, or controls either the exposure start or finish operation by means of the camera shutter or the light source side shutter, thereby shortening the period of tissue illumination and thermal exposure.
In photographic systems of this type, an automatic exposure control device is typically combined with the above-described light source control device to simplify the photographic operation. The automatic exposure control device is so desinged that part of the light reflected from the object is received by a photosensitive element whose output current is integrated, and when the integration value reaches a certain level a film exposure completion signal is produced. With an automatic exposure control device and a light source control device used in combination, high intensity light is applied to the body tissue or object such that the film exposure can be effected with the camera shutter opened (that is, the integration operation is commenced simultaneously with the opening of the camera shutter), whereby the synchronization of the object lighting timing with the photographic timing, and the coincidence of the former with the start of the light quantity integration, can be obtained.
In such a conventional device, the light quantity integration preparation is completed or the input gate of the integrator is closed before the film exposure is commenced. Therefore, during the period of time from the preparation completion to when the object lighting is fully implemented, noise signals and drifts may occur in the automatic exposure control circuit, and this electrical instability results in exposure control errors.